Autistic syndrome (or autism) is a pervasive developmental behavioral disorder of very early onset that is characterized by a fundamental lack of normal interest in other people. (Original description, Kanner L. Autistic disturbances of affective contact. Nervous Child 1943;2:217-250.) The recent diagnostic criteria (DSM IV) for autistic disorder are shown in Table 3 below from the American Psychiatric Association.sup.1.
Epidemiologic studies suggested a prevalence rate of autistic behavior of approximately 2 to 5 cases in 10,000, however, recent surveys including the entire spectrum of the disease indicate that rates of 15 per 10,000 are a more accurate disease prevalence.sup.2,3. Such figures indicate that this disorder affects four hundred thousand Americans, with significant social and public health costs.
Despite the substantial body of evidence implicating neurobiological factors in the pathogenesis, precise etiologic mechanisms of autism have yet to be identified. In the absence of a clear etiology, although both behavioral and medical interventions are available to improve learning and behavior, there is no evidence of a cure for autism, nor any efficient psychopharmacological treatments for the core symptoms.
Autism is a syndrome with multiple etiologies, as is made clear both by the evidence of neurobiological research and by the catalog of disorders that are present with autistic behaviors.sup.4. Based on clinical observations, there are subgroups and subtypes of subjects with significantly different patterns of strengths and deficits, different patterns of comorbidity, levels of severity, and different psychological/cognitive profiles. The response to therapeutic trials also showed a wide variety of outcomes, which may support the possibility that there are multiple etiologies for autism. Although we know that genetic, infectious, metabolic, immunologic, neurophysiological, and environmental causes may lead to similar patterns of altered development with autistic behavior, the recognition of these clear neuropathological disorders does not help us to understand the basic pathogenic mechanism of autism.
There is no clear biological marker of autism to allow early diagnosis or screening of this disease even though it is generally believed that early recognition and management is crucial in the prognosis. Under these circumstances, every clinical observation is important and may lead us to a better understanding of this disorder.
While the specific neuropathological mechanism that produces autism is unknown, it is thought to be the result of a dysfunction of particular groups of neurons in the central nervous system. The primary structures implicated in the autistic disorder are the cerebellum, cerebral cortex, and medial temporal structures. One study showed a significant loss of Purkinje cells, and to lesser extent, of granular cells in the cerebellar hemispheres of six autistic subjects.sup.5. Studies of two patients with autism showed that the hippocampal pyramidal neurons in the CA1 and CA4 fields displayed a decrease in dendritic branching.sup.6. Metabolic dysfunction of cortical areas was found through measurements by Single Photon Emission Computed Tomography (SPECT).sup.7. In addition, involvement of the medial temporal lobe has been implicated by autopsy studies demonstrating increased cell density, and small cell size in the hippocampus, amygdala, enthorhinal cortex and septal nuclei.sup.8. An additional argument for the temporal lobe involvement is the case report describing a child with a left lateral oligodendroglioma, who fulfilled the criteria of autistic behavior.sup.9. This case supports the hypothesis that damage to mesial-temporal structures at an early developmental period may lead to the autistic syndrome. Experimental evidence also supports this argument. A two-stage removal of the amygdalo-hippocampal complex in newborn monkeys resulted in behavioral changes (abnormalities of social interactions, absence of facial and body expressions and stereotypical behavior), resembling autism in children.sup.10. It is important to note that subgroups of autistic children displayed distinct patterns of brain activity in the frontal and temporal regions. Differences were more prominent in the left than the right hemisphere.sup.11. Four adult patients with autism had regionally decreased blood flow in the right lateral temporal, and in the right, left, and midfrontal lobes compared with controls.sup.12.
The neurobiological etiology of autism is supported by the observation that epilepsy is a common concomitant of autism.sup.13, affecting approximately one-third of adults who had childhood autism which usually had began in infancy or adolescence. In addition, different subgroups of patients have exhibited a variety of biochemical/immunological abnormalities. For example, in 20-40% of patients, whole blood serotonin levels are elevated.sup.14, and platelet serotonin is altered. Other observations include changes in the levels of dopamine-beta-hydroxylase (DBH) in plasma.sup.15, elevations in the levels of beta-endorphin, norepinephrine, arginine-vasopressin, and abnormally low levels of adrenocorticotropic hormone in 70% of autistic children.sup.16, however, there are no supporting data for the autoimmune mechanism and the therapeutic trials with steroid treatment are disappointing so far.
Drug trials for autism have included tests of the effects of dopamine agonists, and antagonists to dopamine, serotonin and opiates, as well as beta blockers, ACTH analogs, and oxytocin.sup.18. Most of these treatments were associated with some beneficial effect in small groups of patients. The broad range of biochemical abnormalities that stimulated this wide diversity of pharrnacotherapeutic trials is a clear indication that we are still far from the understanding the main pathological events in the brain resulting in autistic behavior.
Two recent hypotheses of autism are the opioid- and the immune theory. The opioid theory is based on the observation that the main features of autism are similar to features of opiate addiction. The autistic-like behavior elicited by opiate administration include: reduced socialization, affective lability, repetitive stereotyped behavior, episodes of increased motor activity, diminished crying, insensitivity to pain, and poor clinging. Motivated by this similarity, clinical trials have been conducted by using an opioid antagonist, naltrexone, in autistic patients. In an open trial, 8 to 10 children were judged to show a positive response to naltrexone.sup.9. However, more recent double-blinded studies found that naltrexone treatment failed to produce significant changes in social behavior.sup.20.
Other researchers suppose that the opioids are derived from food sources. The enzymatic digest of casein and gluten contains peptides with opioid activity.sup.21. Fukudome and Yoshikawa isolated four opioid peptides from the digest of wheat gluten.sup.2. One of these peptides occurred in 15 different sites in the primary structure of glutenin, which is high molecular weight protein in wheat and considered as innocent protein in celiac disease. An additional indirect argument for the possible role of exogenous peptides was the presence of an abnormal urinary peptide pattern in patients with autism.sup.23. Although there is no scientific evidence that these exogenous peptides may enter the bloodstream, open clinical trials in Norway have been undertaken with the long-term elimination of gluten and casein from the diet of patients with autistic behavior and found only mild improvement.sup.24. As can be seen by prior research studies, while administration of opioids causes autistic behavior trials with specific and very restricted diets and opioid antagonists have not resulted in evident improvement in the behavior and health of autistic patients.
Certain immune-system abnormalities have been observed in connection with autism, such as cell-mediated immune response to human myelin basic protein.sup.17 and changes in the percentage of different subpopulations of lymphocytes.sup.25. The followers of immunopathogenesis theory are trying to use large doses of steroids. The administration of steroids resulted in some improvement in the behavior of few patients. However, to maintain this improvement, continuous administration of large doses of steroid were necessary, accompanied by all the side effect of chronic steroid administration. A tapering of the therapeutic dosage of steroid resulted in an immediate relapse.
A significant portion of patients with autistic behavior also suffer from mild gastrointestinal 5 symptoms, such as abdominal distension, constipation, or chronic loose stools. Although these gastrointestinal problems are well known, they are not considered as important clinical features of the autistic syndromes, nor have they been treated except symptomatically. Autistic children with chronic diarrhea are not referred routinely to a pediatric gastroenterologist. In a recent study, 43% of patients had altered intestinal permeability.sup.26, which is a strong argument for an intestinal dysfunction in a significant portion of autistic patients.
Secretin is a 27-amino acid peptide hormone produced by the S-dells of the small intestine that are spatially distributed from the upper crypt to the villus tip, being particularly numerous in the upper two-thirds of the villi.sup.27. The release of secretin is increased by the products of protein digestion, acid bathing, fat, sodium-oleate, bile and herbal extracts (see FIG. 1A) . Secretin increases the secretion of bicarbonate in the pancreas and biliary tract, resulting in secretion of a watery, alkaline pancreatic fluid (see FIG. 1B). The effect of secretin on the pancreas and bile duct is mediated primarily by secretin-induced elevation of cyclic AMP.sup.29, and does not involve the inositol phosphates signal transduction pathway (see FIG. 1C).
Secretin regulates the growth and development (enzyme composition) of the stomach, small intestine, and pancreas , and stimulates pancreatic fluid secretion, and bile secretion.sup.31. In addition, secretin has secretory, motility and circulatory effects in the gastrointestinal tract. Secretin stimulates immunoglobulin excretion through bile.sup.32. Secretin increases superior mesenteric blood flow, and its distribution within the mucosa and submucosa.sup.33, as well as lymph flow.sup.34 (see Table 1).
Thus far, the clinical uses of secretin are based on its secretory and vascular effects. The two most important diagnostic applications are the examination of pancreatic function, and the diagnosis of gastrinoma. There is no accepted therapeutic use. A trial to use secretin in intrahepatic cholestasis in small numbers of patients initially was encouraging.sup.35, however, a double-blind placebo-controlled multicentric trial found no statistically significant differences in the reduction of serum bilirubin levels between secretin and placebo groups.sup.36.
The structure of porcine secretin has been known for some time and it has been isolated from porcine intestine, and has been found to be constituted by a peptide composed of 27 amino acid residues.sup.37. Moreover, it has been found that bovine and porcine secretins are identical but that they are markedly different from chicken secretin.sup.38. Although bovine and porcine secretins behave identically with human secretin in some respects they are not structurally identical (4,806,336 Carlquist et al. 2/89). U. S. Pat. No. 4,806,336 (Carlquist et al.) discloses the chemical composition of human secretin, a method for administering secretin for diagnostic use in determining pancreatic or gallbladder function, and a method for stimulating pancreatic secretion in man.
There is no published information suggesting a direct relationship between autism and secretin. However, it has been proposed that secretin and receptors of secretin are present in the brain areas that are thought to be involved in autism. Although exactly how secretin works in the brain is not yet fully understood, it seems likely that secretin regulates neurotransmitters and influences the function of a variety of cells, especially in the "hippocampal" and "amygdaloid" brain areas, where seem to be impaired in autism. (See Table 2.)
Our observations described in detail herein suggest that secretin is effective in the treatment of both gastrointestinal and behavioral/developmental problems in some children with autism. We observed that a group of young autistic children with chronic diarrhea, while they were undergoing tests involving an injection of secretin, had an extraordinary increase in the production of fluid from their pancreas. During the follow- up clinical visits these same children showed impressive progress in their social, behavioral and language skills, which appears so far to be permanent. We also found that the children who showed these responses to injected secretin produced only small amounts of their own secretin, and when given a dose of secretin by injection, they were able to produce an elevation in the blood level of another hormone, serotonin, which has effects on the brain.
These observations demonstrate the close relationship between secretin and serotonin in a group of autistic children. Our findings suggest that there are two subgroups of autistic patients, distinguished on the basis of gastrointestinal symptoms, their own blood secretin levels, the increase in serotonin level after secretin injection and the quantity and quality of fluid produced for secretin stimulation. In addition, we found high prevalence of other gastrointestinal abnormalities (inflammation in the esophagus, digestive enzyme deficiencies) in children with autistic behavior which adds further support to a relationship between the presence of gastrointestinal dysfunctions and autism.
Thus, we have discovered that the gastrointestinal/brain hormone secretin has a beneficial therapeutic effect on the gastrointestinal and brain function in certain autistic children. Our findings are the first clear evidence for an association between brain and gastrointestinal dysfunctions in autistic children.
With no prior findings of secretin having the capability to influence human behavior, there has been no research into the effect of secretin on autistic disorder. This invention is based on the unique and dramatic clinical observations of the effect of secretin administered for the diagnostic evaluation of gastrointestinal function in children with autistic behavior. These observations included:
(1) significant improvement in the social communication (language) and behavioral skills; and PA1 (2) hypersecretion of pancreato-biliary fluid in children with autism and chronic loose stools.
These observations described here open an entirely new direction in the autism research and may help to understand the pathogenesis of this disease. In addition, it may lead to a better understanding of the role of gut peptide hormones in the brain function. The existence of the gut-brain axis has been hypothesized, however, there was no clear clinical entity associated with this axis until now. This observation is the first clear evidence for an association between gastrointestinal and brain dysfunctions.